1. Field of the Invention
This invention relates generally to a method and apparatus for testing networks of a multilayer ceramic substrate (MLC) during a manufacture thereof and, more particularly, to a shorting pad actuator adapted for use therewith.
2. Discussion of the Related Art
Substrate testers are known in the art for performing network integrity tests on substrates, such as multilayer ceramic substrates (MLCs). A substrate refers to a packaging unit that provides an interface between a semiconductor chip (e.g. a very large scale integrated (VLSI) circuit chip) and a higher level packaging unit (e.g., a printed circuit board). A network is generally defined by a set of one or more electrically connected common points on a substrate. Networks are used to distribute electrical signals and voltages externally and/or internally about the substrate in accordance with the requirements of a particular integrated circuit chip. Substrate testers are used during substrate manufacturing to guarantee that there are no process or design created defects (corresponding to opens or shorts) on a particular substrate being tested. Typically, a substrate tester performs a test using a particular contacting scheme. A test matrix scanner is then used to provide an electrical stimulus on each point of the networks contacted by the contacting scheme and then systematically scans the remaining points in the test matrix to guarantee all desired connections exist (opens test) and that there are no unwanted connections (shorts), as the case may be.
In current manufacturing techniques of MLC substrates, there is a need to improve the accuracy and cost structure of substrate locators in an effort to satisfy more stringent manufacturing process requirements. Conventional substrate locators require many moving parts which disadvantageously contribute to tolerance build-ups, inaccuracies, and thus higher manufacturing costs. Conventional substrate locators also use many high precision parts, which are not performance efficient or cost efficient for meeting the current manufacturing requirements. For example, multi-cam drive assemblies are exceedingly costly in terms of their use in the manufacturing process.
Current state of the art substrate locators furthermore include a number of moving parts, which may include parts such as precision cam slots, cam followers, gears, etc.. The moving parts contribute to a build up of tolerances. This build up of tolerances prevents a precise and absolute locating and positioning by the locator with respect to a centering of the substrate parts over or under a workstation, wherein the workstation requires extreme positioning accuracy and repeatability. The workstation may also include a high speed substrate tester (HSST) which has traditionally been characteristically large and slow.
Features on MLC substrate s are very small and in close proximity to one another. For example, any one particular MLC substrate may include more than one thousand pin or pad connections in an area on the order of one-quarter square inch of space, as can been realized in the current state of art for MLC substrates. It is thus very critical to align the substrate parts in a repeatable manner, for example, with respect to a testing and a placement of test contacts, or other processing and manufacturing options, such as chip placement, discrete wiring, etc.
In addition, in today's MLC substrate manufacturing environment, a wide variety of substrate sizes are manufactured. For testing of the various sized substrates, the substrate tester must undergo a product changeover to accommodate a substrate of a different size from that which it was previously set up for. This has lead to the use of expensive multiple hardware for making a product changeover, further resulting in a lengthy and inefficient changeover process.
Yet another aspect of known substrate testers is that the testers for implementing shorting pad testing fail to equally distribute or align forces across an array of network terminals on a substrate under test. In other words, the contact platens used for providing necessary forces are generally not parallel with each other, thus leading to an uneven distribution of contacting force upon the substrate under test. In addition, the substrate under test may be supported in such a way that undesirably cocks or tilts the substrate. Contacting forces applied under the above conditions are thus not applied evenly across an entire contacting area of the substrate under test. Another example of an uneven distribution of contacting forces occurs if the substrate under test varies in thickness from one edge to another. The unevenness leads to marginal test results, thereby producing an increased probability of undesired detection of false open circuitry.
Furthermore, in addition to the above discussion, physical space limitations of the tester apparatus, and more particularly, for a substrate locating and clamping mechanism and a shorting pad actuator, are of concern. A large pressure is generally required for use in shorting pad testing of a substrate. It is thus desirable to have the shorting pad actuator of the substrate tester and the locating and clamping mechanism as close to one another as possible to enable the large pressure to develop while accurately positioning and locating the substrate under test.
Referring now to FIG. 1, the problem of a test contact head A1 being out-of-parallel with a substrate A2 under test is exemplified and briefly discussed. As shown, a force F1 is applied to the test head A1. A substrate A2 under test is supported upon a fixed product support A3. The test head A2, however, does not contact the substrate A2 under test evenly because of the test contact head A1 being out-of-parallel with the substrate support A3. Such an out-of-parallel condition (as noted by A4) undesirably leads to erroneous test results, for example, since the networks on the substrate A2 may not all be properly contacted.
It would thus be desirable to provide a shorting pad actuator which overcomes the out-of-parallel problems as discussed above, while requiring a minimum amount of space in the tester apparatus.